Fix variations crashes when the chosen trial group is not in study.

components/variations/variations_seed_processor.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/variations/variations_seed_processor.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <vector>
@@ skipping 83 matching lines @@
     ApplyUIStringOverrides(experiment, override_callback);
   }
 }
 
 // Registers feature overrides for the chosen experiment in the specified study.
 void RegisterFeatureOverrides(const ProcessedStudy& processed_study,
                               base::FieldTrial* trial,
                               base::FeatureList* feature_list) {
   const std::string& group_name = trial->GetGroupNameWithoutActivation();
   int experiment_index = processed_study.GetExperimentIndexByName(group_name);
-  // The field trial was defined from |study|, so the active experiment's name
-  // must be in the |study|.
-  DCHECK_NE(-1, experiment_index);
+  // If the chosen experiment was not found in the study, simply return.
+  // Although not normally expected, but could happen in exception cases, see
+  // tests: ExpiredStudy_NoDefaultGroup, ExistingFieldTrial_ExpiredByConfig
+  if (experiment_index == -1)
+    return;
 
   const Study& study = *processed_study.study();
   const Study_Experiment& experiment = study.experiment(experiment_index);
 
   // Process all the features to enable.
   int feature_count = experiment.feature_association().enable_feature_size();
   for (int i = 0; i < feature_count; ++i) {
     feature_list->RegisterFieldTrialOverride(
         experiment.feature_association().enable_feature(i),
         base::FeatureList::OVERRIDE_ENABLE_FEATURE, trial);
@@ skipping 201 matching lines @@
     // params won't be registered under the correct key.
     const std::string& group_name = trial->group_name();
 
     // Don't try to apply overrides if none of the experiments in this study had
     // any.
     if (!has_overrides)
       return;
 
     // UI Strings can only be overridden from ACTIVATION_AUTO experiments.
     int experiment_index = processed_study.GetExperimentIndexByName(group_name);
-
-    // The field trial was defined from |study|, so the active experiment's name
-    // must be in the |study|.
-    DCHECK_NE(-1, experiment_index);
-
-    ApplyUIStringOverrides(study.experiment(experiment_index),
-                           override_callback);
+    // If the chosen experiment was not found in the study, simply return.
+    // Although not normally expected, but could happen in exception cases, see
+    // tests: ExpiredStudy_NoDefaultGroup, ExistingFieldTrial_ExpiredByConfig
+    if (experiment_index != -1) {
+      ApplyUIStringOverrides(study.experiment(experiment_index),
+                             override_callback);
+    }
   }
 }
 
 }  // namespace variations